a) Field of the Invention
The invention relates to an auto-drive control unit for vehicles, and more particularly to unit for controlling mode changeover from auto-drive to manual drive.
b) Description of the Related Art
A conventional automatic driving system is known that controls vehicle speed and steering angle based on information from various sensors and switches between an auto-drive mode and a manual drive mode by a changeover switch when necessary. There is, however, a significant problem in determining when the changeover shall be made as a driver is required to operate the steering wheel with high driving skill immediately after changing mode changes if the auto-drive mode is switched to the manual drive mode when the vehicle's running is not stable. For example, Japanese Patent Laid-Open Publication No. Hei 3-282713 discloses a technology where switching from the auto-drive mode to the manual drive mode is prohibited when the vehicle is running on a curved road.
However, conditions where a vehicle's running is not stable are not limited to curved roads, but also include a straight roads. For example, running becomes unstable due to significant disturbances when a vehicle running on a straight road is exposed to a side wind, a vehicle is running on uneven road surfaces, or a vehicle is running across rain puddles. If auto-drive is switched to manual drive under such conditions, the driver may be required to unexpectedly operate the steering wheel.